We would like to know some more information about your concern. Do you plan to design a custom board for the Edison?
If you want to update the firmware on the Intel® Edison board via USB, you need to use only the USB OTG port.
Additionally, about using WiFi to update the Edison, we recommend you read this thread https://communities.intel.com/thread/105153, and also we find this information https://gist.github.com/skvark/794217634c5024da9052 that could be useful.
We hope this information helps, please let us know if you have any question.
I am still trying to digest your suggestion, but I got side track to another project at this moment